No, apple cider vinegar does not hurt poinsettias
(Euphorbia pulcherrima).
Specifically, apple cider vinegar is acidic, and poinsettias are
acid-loving plants. They prefer soil pH ranges between 4.5 and 6.5,
that is, between the quite acidic to the lower limits of the
neutral zone that so many ornamentals favor. Apple cider vinegar is
quite effective at sanitizing soil, and poinsettias are sensitive
to less than sanitary conditions. So poinsettias like their soil
acidic and clean, and apple cider vinegar fits the bill on both
counts.

Apple cider or white vinegar are acidic that can emulsify the
natural oils to hydroxyls and with further reaction turn into
salts.Both Apple cider or white vinegar are mild acid that clean
the hair to shine but can not help to cure dandruff dryness of the
scalp. The scalp pH is high and is cleaned or sometimes causes mild
irritation .